Dull work for old king in Germany (5)
I believe the answer is:
grind
'dull work' is the definition.
'grind' can be an answer for 'work' (grind is a kind of work). I am unsure of the 'dull' bit.
'old king in germany' is the wordplay.
'old king' becomes 'GR' (Georgius Rex, Latin for King George).
'germany' becomes 'd' (vehicle registration code for Deutschland).
'gr'+'in'+'d'='GRIND'
'for' acts as a link.
Can you help me to learn more?
(Other definitions for grind that I've seen before include "Monotonous, routine work" , "work for teeth?" , "Hard work, as in mill" , "Harshly rub together" , "drudgery" .)